Automated manufacturing processes frequently employ multiple manufacturing stations, with parts in process being transported from one station to the next on a conveyor belt. For example, it is customary in the manufacture of cylindrical metal pins or shafts to route the individual parts in process through a series of through-feed grinders, each grinder removing material until the desired diameter and surface finish are achieved. Ideally, the manufacturing stations would be synchronized to maximize throughput of parts without backing up parts on the conveyor belt. However, the throughput of an individual manufacturing station often changes due to wear (particularly in grinding or cutting operations), and a back-up at one station can cause jam-ups at other upstream stations. Accordingly, manual controls are usually provided to enable an operator to adjust the conveyor speed to suitably balance the line and prevent jam up of parts between stations. Obviously, manual control of line speed is undesired because of the labor cost and because of the difficulty of manually optimizing the control.